The present invention relates generally to apparatus for measuring the resistance of a load, and more particularly to apparatus for measuring the resistance of breaker contacts utilized for switching electrical power.
The breaker resistance of contacts for use in switching and distributing electrical power is required to be determined during production of such breaker contacts as well as in the field for preventive maintenance. The measurement of breaker contact resistance must be extremely accurate in order to provide ratings in accordance with existing industry standards. The standards generally require that high voltage power circuit breaker contact resistance be measured by applying 100 amps across the circuit breaker terminals. The measurements required by the standards have presented problems in that there has not been available a lightweight, portable battery-operated unit which has been able to supply the necessary amperage with consistently good accuracy. Prior art methods have used very high current power sources, such as direct current welders, and have used measuring methods with limited accuracy such as millivolt meters. The weight of these units is extremely heavy, and therefore these units have been stationary in nature. Accordingly, they are limited to production testing and not very useful in the field.
Another method utilized in the prior art was that as exemplified by the U.S. Patent to Alber et al, Pat. No. 3,816,812. This measuring apparatus has not proven entirely satisfactory, in that the apparatus described therein is not utilized to determine resistances in the micro-ohm range; rather, the measuring apparatus therein is constructed to be a millivolt tester.